1. Field of the Invention
The subject matter of the present invention relates to modified epoxy thermosetting adhesive compositions useful for bonding of various composite or metal substrates, and having improved characteristics. More particularly, the subject matter relates to thermosetting compositions containing nano-sized core-shell particles in combination with elastomers and/or thermoplastics, to provide synergistic and superior toughness, high temperature shear properties, high glass transition temperature, and low water absorption. These new compositions are suitable for hostile environments and demanding applications in various industries, as structural adhesives and matrix resins for fiber reinforced epoxy prepregs.
2. Description of the Related Art
Numerous compositions and processes are described in the art for making and using a wide variety of epoxy-based compositions and other resins and additives in an effort to improve the shear strength, impact resistance and other key properties of adhesives useful in adhering, filling and making composite and metal structures. For example, patents which describe components for the formulation of adhesive compositions and the use of such compositions to adhere various substrates to each other and to provide structural reinforcement include U.S. Pat. Nos. 5,028,478; 5,087,657; 5,242,748; 5,278,257; 5,290,857; 5,605,745; 5,686,509; 5,334,654; 6,015,865; 6,037,392; 6,884,854; and 6,776,869; and U.S. Patent Application Publication Nos. 2005/0022929; and 2008/0188609.
Although adhesive compositions and composite structures with improved toughness have been disclosed previously, there has been some sacrifice with regard to other physical properties of the compositions, including, for example, a reduction in glass transition temperatures together with an increase in creep at high temperatures. For example, adhesive compositions to date suffer from a decrease in high temperature properties (e.g., shear properties) as the toughness (peel) is increased. Further difficulties with such adhesive compositions and composites can include a loss in stiffness, adhesive failure that occurs between substrates formed of dissimilar materials and/or resins, and property deterioration during use due to poor solvent resistance.
Accordingly, the adhesive compositions and methods presently available for producing toughened composites and for bonding of various composite and/or metal substrates require further improvement. Thermosetting adhesive compositions having improved resistance to impact, and having improved toughness and shear properties at high temperatures would be a useful advance in the art and could find rapid acceptance in the aerospace and high performance automotive industries, among others.